This invention relates to a new and improved catheter, and more specifically to a catheter which occupies a larger cross sectional area than the cannula through which it fits. This enables the catheter to be inserted through a cannula having a smaller cross section than the catheter itself and into a vein orifice of smaller size than the catheter.
The problem which occurs when using a conventional catheter and cannula arrangement is the possibility that because the cannula has a larger diameter than the catheter, it will obviously create a larger perforation in the vein than the catheter; consequently, the catheter may slip out of the oversized perforation. Another problem associated with catheters is the fact that veins tend to be elliptical in cross section, however, catheters are manufactured with a circular configuration. Hence, even if a somewhat undersized catheter does not present a problem, where a catheter and vein have mismatched shapes, a potentially loose fit is possible. A loose fit may result in intravenous leakage or in the catheter simply slipping out from a vein, even when seemingly adequately secured.